science as knowledge derived from the facts of：科學(xué)作為知識(shí)源于事實(shí)

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FromA.F.Chalmers,Whatisthisthingcalledscience?

Scienceasknowledgederivedfromthefactsofexperience

Awidelyheldcommonsenseviewofscience

Apopularconceptionofthedistinctivefeatureofscientificknowledgeiscapturedbytheslogan"scienceisderivedfromthefacts".Wewillfindthatmuchofwhatistypicallytakentobeimpliedbytheslogancannotbedefended.Nevertheless,wewillfindthatthesloganisnotentirelymisguided.

Whenitisclaimedthatscienceisspecialbecauseitisbasedonthefacts,thefactsarepresumedtobeclaimsabouttheworldthatcanbedirectlyestablishedbyacareful,unprejudiceduseofthesenses.Scienceistobebasedonwhatwecansee,hearandtouchratherthanonpersonalopinionsorspeculativeimaginings.Ifobservationoftheworldiscarriedoutinacareful,unprejudicedwaythenthefactsestablishedinthiswaywillconstituteasecure,objectivebasisforscience.If,further,thereasoningthattakesusfromthisfactualbasistothelawsandtheoriesthatconstitutescientificknowledgeissound,thentheresultingknowledgecanitselfbetakentobesecurelyestablishedandobjective.

Theaboveremarksarethebarebonesofafamiliarstorythatisreflectedinawiderangeofliteratureaboutscience."Scienceisastructurebuiltuponfacts"writesJ.J.Davies(1968,p.8)inhisbookonthescientificmethod,athemeelaboratedonbyH.D.Anthony(1948,p.145):

ItwasnotsomuchtheobservationsandexperimentswhichGalileomadethatcausedthebreakwithtraditionashisattitudetothem.Forhim,thefactsbasedonthemweretakenasfacts,andnotrelatedtosomepreconceivedidea...The.factsofobservationmight,ormightnot,fitintoanacknowledgedschemeoftheuniverse,buttheimportantthing,inGalileo'sopinion,wastoacceptthefactsandbuildthetheorytofitthem.

Anthonyherenotonlygivesclearexpressiontotheviewthatscientificknowledgeisbasedonthefactsestablishedbyobservationandexperiment,butalsogivesahistoricaltwisttotheidea,andheisbynomeansaloneinthis.Aninfluentialclaimisthat,asamatterofhistoricalfact,modemsciencewasbornintheearlyseventeenthcenturywhenthestrategyoftakingthefactsofobservationseriouslyasthebasisforsciencewasfirstseriouslyadopted.Itisheldbythosewhoembraceandexploitthisstoryaboutthebirthofsciencethatpriortotheseventeenthcenturytheobservablefactswerenottakenseriouslyasthefoundationforknowledge.Rather,sothefamiliarstorygoes,knowledgewasbasedlargelyonauthority,especiallytheauthorityofthephilosopherAristotleandtheauthorityoftheBible.Itwasonlywhenthisauthoritywaschallengedbyanappealtoexperience,bypioneersofthenewsciencesuchasGalileo,thatmodernsciencebecamepossible.

Thefollowingaccountoftheoft-toldstoryofGalileoandtheLeaningTowerofPisa,takenfromRowbotham(1918,pp.27—9),nicelycapturestheidea.

Galileo'sfirsttrialofstrengthwiththeuniversityprofessorswasconnectedwithhisresearchesintothelawsofmotionasillustratedbyfallingbodies.ItwasanacceptedaxiomofAristotlethatthespeedoffallingbodieswasregulatedbytheirrespectiveweights:thus,astoneweighingtwopoundswouldfalltwiceasquickasoneweighingonlyasinglepoundandsoon.Nooneseemstohavequestionedthecorrectnessofthisrule,untilGalileogaveithisdenial.Hedeclaredthatweighthadnothingtodowiththematter,andthattwobodiesofunequalweightwouldreachthegroundatthesamemoment.AsGalileo'sstatementwasfloutedbythebodyofprofessors,hedeterminedtoputittoapublictest.SoheinvitedthewholeUniversitytowitnesstheexperimentwhichhewasabouttoperformfromtheleaningtower.Onthemorningofthedayfixed,Galileo,inthepresenceoftheassembledUniversityandtownsfolk,mountedtothetopofthetower,carryingwithhimtwoballs,oneweighingonehundredpoundsandtheotherweighingonepound.Balancingtheballscarefullyontheedgeoftheparapet,herolledthemovertogether;theywereseentofallevenly,andthenextinstant,withaloadclang,theystruckthegroundtogether.Theoldtraditionwasfalse,andmodernscience,inthepersonoftheyoungdiscoverer,hadvindicatedherposition.

TwoschoolsofthoughtthatinvolveattemptstoformalizewhatIhavecalledacommonviewofscience,thatscientificknowledgeisderivedfromthefact,aretheempiricistsandthepositivists.TheBritishempiricistsoftheseventeenthandeighteenthcenturies,notablyJohnLocke,GeorgeBerkeleyandDavidHume,heldthatallknowledgeshouldbederivedfromideasimplantedinthemindbywayofsenseperception.Thepositivistshadasomewhatbroaderandlesspsychologicallyorientatedviewofwhatfactsamountto,butsharedtheviewoftheempiriciststhatknowledgeshouldbederivedfromthefactsofexperience.

Thelogicalpositivists,aschoolofphilosophythatoriginatedinViennainthe1920s,tookupthepositivismthathadbeenintroducedbyAugusteComteinthenineteenthcenturyandattemptedtoformalizeit,payingcloseattentiontothelogicalformoftherelationshipbetweenscientificknowledgeandthefacts.Empiricismandpositivismsharethecommonviewthatscientificknowledgeshouldinsomewaybederivedfromthefactsarrivedatbyobservation.

Therearetworatherdistinctissuesinvolvedintheclaimthatscienceisderivedfromthefacts.Oneconcernsthenatureofthese"facts"andhowscientistsaremeanttohaveaccesstothem.Thesecondconcernshowthelawsandtheoriesthatconstituteourknowledgearederivedfromthefactsoncetheyhavebeenobtained.Wewillinvestigatethesetwoissuesinturn.

Threecomponentsofthestandonthefactsassumedtobethebasisofscienceinthecommonviewcanbedistinguished.Theyare:

(a)Factsaredirectlygiventocareful,unprejudicedobserversviathesenses.

(b)Factsarepriortoandindependentoftheory.

(c)Factsconstituteafirmandreliablefoundationforscientificknowledge.

Asweshallsee,eachoftheseclaimsisfacedwithdifficultiesand,atbest,canonlybeacceptedinahighlyqualifiedform.

Seeingisbelieving

Partlybecausethesenseofsightisthesensemostextensivelyusedtoobservetheworld,andpartlyforconvenience,Iwillrestrictmydiscussionofobservationtotherealmofseeing.Inmostcases,itwillnotbedifficulttoseehowtheargumentpresentedcouldbere-castsoastobeapplicabletotheothersenses.

Asimpleaccountofseeingmightrunasfollows.Humansseeusingtheireyes.Themostimportantcomponentsofthehumaneyearealensandaretina,thelatteractingasascreenonwhichimagesofobjectsexternaltotheeyeareformedbythelens.Raysoflightfromaviewedobjectpassfromtheobjecttothelensviatheinterveningmedium.Theseraysarerefractedbythematerialofthelensinsuchawaythattheyarebroughttoafocusontheretina,soforminganimageoftheobject.Thusfar,thefunctioningoftheeyeisanalogoustothatofacamera.Abigdifferenceisinthewaythefinalimageisrecorded.Opticnervespassfromtheretinatothecentralcortexofthebrain.Thesecarryinformationconcerningthelightstrikingthevariousregionsoftheretina.Itistherecordingofthisinformationbythebrainthatconstitutestheseeingoftheobjectbythehumanobserver.Ofcourse,manydetailscouldbeaddedtothissimplifieddescription,buttheaccountofferedcapturesthegeneralidea.

Twopointsarestronglysuggestedbytheforgoingaccountofobservationthroughthesenseofsightthatareincorporatedintothecommonorempiricistviewofscience.Thefirstisthatahumanobserverhasmoreorlessdirectaccesstoknowledgeofsomefactsabouttheworldinsofarastheyarerecordedbythebrainintheactofseeing.Thesecondisthattwonormalobserversviewingthesameobjectorscenefromthesameplacewill"see"thesamething.Anidenticalcombinationoflightrayswillstriketheeyesofeachobserver,willbefocusedontheirnormalretinasbytheirnormaleyelensesandgiverisetosimilarimages.Similarinformationwillthentraveltothebrainofeachobserverviatheirnormalopticnerves,resultinginthetwoobserversseeingthesamething.

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Derivingtheoriesfromthefactsusinginduction

Babylogic

Logicisconcernedwiththedeductionofstatementsfromother,given,statements.Itisconcernedwithwhatfollowsfromwhat.Noattemptwillbemadetogiveadetailedaccountandappraisaloflogicordeductivereasoninghere.Rather,Iwillmakethepointsthatwillbesufficientforourpurposewiththeaidofsomeverysimpleexamples.

Hereisanexampleofalogicalargumentthatisperfectlyadequateor,tousethetechnicaltermusedbylogicians,perfectlyvalid.

Example1

1.Allbooksonphilosophyareboring.

2.Thisbookisabookonphilosophy.

3.Thisbookisboring.

Inthisargument,(1)and(2)arethepremisesand(3)istheconclusion.Itisevident,Itakeit,thatIF(l)and(2)aretruethen(3)isboundtobetrue.Itisnotpossiblefor(3)tobefalseonceitisgiventhat(1)and(2)aretrue.Toassert(1)and(2)astrueandtodeny(3)istocontradictone’sself.

Thisisthekeyfeatureofalogicallyvaliddeduction.Ifthepremisesaretruethentheconclusionmustbetrue.Logicistruthpreserving.

AslightmodificationofExample(1)willgiveusaninstanceofanargumentthatisnotvalid.

Example2

1.Manybooksonphilosophyareboring.

2.Thisbookisabookonphilosophy.

3.Thisbookisboring.

Inthisexample,(3)doesnotfollowofnecessityfrom(1)and(2).EVENIF(l)and(2)aretrue,thenthisbookmightyetturnouttobeoneoftheminorityofbooksonphilosophythatarenotboring.Accepting(1)and(2)astrueandholding(3)tobefalsedoesnotinvolveacontradiction.Theargumentisinvalid.

Thereadermaybynowbefeelingbored.Experiencesofthatkindcertainlyhaveabearingonthetruthofstatements(1)and(3)inExample1andExample2.Butapointthatneedstobestressedhereisthatlogicaldeductionalonecannotestablishthetruthoffactualstatementsofthekindfiguringinourexamples.Allthatlogiccanofferinthisconnectionisthatifthepremisesaretrueandtheargumentisvalidthentheconclusionmustbetrue.Butwhetherthepremisesaretrueornotisnotaquestionthatcanbesettledbyanappealtologic.Anargumentcanbeaperfectlyvaliddeductionevenifitinvolvesafalsepremise.Hereisanexample.

Example3

1.Allcatshavefivelegs.

2.BugsPussyismycat.

3.BugsPussyhasfivelegs.

Thisisaperfectlyvaliddeduction.If(1)and(2)aretruethen(3)mustbetrue.Itsohappensthat,inthisexample(1)and(3)arefalse.Butthisdoesnotaffectthefactthattheargumentisvalid.

Thereisastrongsense,then,inwhichlogicaloneisnotasourceofnewtruths.Thetruthofthefactualstatementsthatconstitutethepremisesofargumentscannotbeestablishedbyappealtologic.Logiccansimplyrevealwhatfollowsfrom,orwhatinasenseisalreadycontainedin,thestatementswealreadyhavetohand.Againstthislimitationwehavethegreatstrengthoflogic,namely,itstruth-preservingcharacter.Ifwecanbesureourpremisesaretruethenwecanbeequallysurethateverythingwelogicallyderivefromthemwillalsobetrue.

Canscientificlawsbederivedfromthefacts?

Withthisdiscussionofthenatureoflogicbehindus,wecansaymoreaboutwhatthepositivistsmeanwhentheysaylawscanbederivedfrothefacts.

Somesimpleexamplesofscientificknowledgewillbesufficient.Letusconsidersomelow-levelscientificlawssuchas"metalsexpandwhenheated"or"acidsturnlitmusred".Thesearegeneralstatements.Theyareexamplesofwhatphilosophersrefertoasuniversalstatements.Theyrefertoalleventsofaparticularkind,allinstancesofmetalsbeingheatedandallinstancesoflitmusbeingimmersedinacid.

Scientificknowledgeinvariablyinvolvesgeneralstatementsofthiskind.Thesituationisquiteotherwisewhenitcomestotheobservationstatementsthatconstitutethefactsthatprovidetheevidenceforgeneralscientificlaws.Thoseobservablefactsorexperimentalresultsarespecificclaimsaboutastateofaffairsthatobtainsataparticulartime.Theyarewhatphilosopherscallsingularstatements.Theyincludestatementssuchas"thelengthofthecopperbarincreasedwhenitwasheated"or"thelitmuspaperturnedredwhenimmersedinthebeakerofhydrochloricacid".

Supposewehavealargenumberofsuchfactsatourdisposalasthebasisfromwhichwehopetoderivesomescientificknowledge(aboutmetalsoracidsinthecaseofourexamples).Whatkindofargumentcantakeusfromthosefacts,aspremises,tothescientificlawsweseektoderiveasconclusions?Inthecaseofourexampleconcerningtheexpansionofmetalstheargumentcanbeschematizedasfollows:

Premises

1.MetalXiexpandedwhenheatedonoccasionTi.

2.MetalX2expandedwhenheatedonoccasionT2.

...

n.MetalXNexpandedwhenheatedonoccasionTN.

Conclusion:Allmetalsexpandwhenheated.

Thisisnotalogicallyvalidargument.Itlacksthebasicfeaturesofsuchanargument.Itissimplynotthecasethatifthestatementsconstitutingthepremisesaretruethentheconclusionmustbetrue.Howevermanyobservationsofexpandingmetalswehavetoworkwith,thatis,howevergreatnmightbeinourexample,therecanbenologicalguaranteethatsomesampleofmetalmightonsomeoccasioncontractwhenheated.Thereisnocontradictioninvolvedinclaimingbasedoninsufficientevidence,aswhen,perhaps,wecondemntheattributionofsomecharacteristictoanentireethnicgroupbasedonsomeunpleasantencounterswithjustonepairofneighbours.Underpreciselywhatcircumstancesisitlegitimatetoassertthatascientificlawhasbeen"derived"fromsomefinitebodyofobservationalandexperimentalevidence?

Afirstattemptatananswertothisquestioninvolvesthedemandthat,ifaninductiveinferencefromobservablefactstolawsistobejustified,thenthefollowingconditionsmustbesatisfied:

1.Thenumberofobservationsformingthebasisofageneralizationmustbelarge.

2.Theobservationsmustberepeatedunderawidevarietyofconditions.

3.Noacceptedobservationstatementshouldconflictwiththederivedlaw.

Condition1isregardedasnecessarybecauseitisclearlynotlegitimatetoconcludethatallmetalsexpandwhenheatedonthebasisofjustoneobservationofanironbar'sexpansion,say,anymorethanitislegitimatetoconcludethatallAustraliansaredrunkardsonthebasisofoneobservationofanintoxicatedAustralian.Alargenumberofindependentobservationswouldappeartobenecessarybeforeeithergeneralizationcanbejustified.Agoodinductiveargumentdoesnotjumptoconclusions.

OnewayofincreasingthenumberofobservationsintheexamplesmentionedwouldbetorepeatedlyheatasinglebarofmetalortocontinuallyobserveaparticularAustraliangettingdrunknightafternight,andperhapsmorningaftermorning.Clearly,alistofobservationstatementsacquiredinsuchawaywouldformaveryunsatisfactorybasisfortherespectivegeneralizations.Thatiswhycondition2isnecessary."Allmetalsexpandwhenheated"willbealegitimategeneralizationonlyiftheobservationsofexpansiononwhichitisbasedrangeoverawidevarietyofconditions.Variouskindsofmetalsshouldbeheated,longbars,shortbars,silverbars,copperbarsetc.shouldbeheatedathighandlowpressuresandhighandlowtemperaturesandsoon.Onlyifonallsuchoccasions,expansionresultsisitlegitimatetogeneralizebyinductiontothegenerallaw.Further,itisevidentthatifaparticularsampleofmetalisobservednottoexpandwhenheated,thenthegeneralizationtothelawwillnotbejustified.Condition3isessential.

Theabovecanbesummedupbythefollowingstatementoftheprincipleofinduction.

IfalargenumberofA'shavebeenobservedunderawidevarietyofconditions,andifallthoseA'swithoutexceptionpossessthepropertyB,thenallA'shavethepropertyB.

Thereareseriousproblemswiththischaracterizationofinduction.Letusconsidercondition1,thedemandforlargenumbersofobservations.Oneproblemwithitisthevaguenessof"large".Areahundred,athousandormoreobservationsrequired?Ifwedoattempttointroduceprecisionbyintroducinganumberhere,thentherewouldsurelybeagreatdealofarbitrarinessinthenumberchosen.Theproblemsdonotstophere.Therearemanyinstancesinwhichthedemandforalargenumberofinstancesseemsinappropriate.Toillustratethis,considerthestrongpublicreactionagainstnuclearwarfarethatwasprovokedbythedroppingofthefirstatomicbombonHiroshimatowardstheendoftheSecondWorldWar.Thatreactionwasbasedontherealizationoftheextenttowhichatomicbombscausewidespreaddestructionandhumansuffering.Andyetthiswidespread,andsurelyreasonable,beliefwasbasedonjustonedramaticobservation.Insimilarvein,itwouldbeaverystubborninvestigatorwhoinsistedonputtinghishandinthefiremanytimesbeforeconcludingthatfireburns.Letusconsideralessfancifulexamplerelatedtoscientificpractice.SupposeIreproducedanexperimentreportedinsomerecentscientificjournal,andsentmyresultsoffforpublication.Surelytheeditorofthejournalwouldrejectmypaper,explainingthattheexperimenthadalreadybeendone!Condition1isriddledwithproblems.

Condition2hasseriousproblemstoo,stemmingfromdifficultiessurroundingthequestionofwhatcountsasasignificantvariationincircumstances.Whatcountsasasignificantvariationinthecircumstancesunderwhichtheexpansionofaheatedmetalistobeinvestigated?Isitnecessarytovarythetypeofmetal,thepressureandthetimeofday?Theansweris"yes"inthefirstandpossiblythesecondcasebut"no"inthethird.Butwhatarethegroundsforthatanswer?Thequestionisimportantbecauseunlessitcanbeansweredthelistofvariationscanbeextendedindefinitelybyendlesslyaddingfurthervariations,suchasthesizeofthelaboratoryandthecolouroftheexperimenter'ssocks.Unlesssuch"superfluous"variationscanbeeliminated,theconditionsunderwhichaninductiveinferencecanbeacceptedcanneverbesatisfied.Whatarethegrounds,then,forregardingarangeofpossiblevariationsassuperfluous?Thecommon-senseanswerisstraightforwardenough.Wedrawonourpriorknowledgeofthesituationtodistinguishbetweenthefactorsthatmightandthosethatcannotinfluencethesystemweareinvestigating.Itisourknowledgeofmetalsandthekindsofwaysthattheycanbeactedonthatleadsustotheexpectationthattheirphysicalbehaviourwilldependonthetypeofmetalandthesurroundingpressurebutnotonthetimeofdayorthecolouroftheexperimenter'ssocks.Wedrawonourcurrentstockofknowledgetohelpjudgewhatisarelevantcircumstancethatmightneedtobevariedwheninvestigatingthegeneralityofaneffectunderinvestigation.

Thisresponsetotheproblemissurelycorrect.However,itposesaproblemforasufficientlystrongversionoftheclaimthatscientificknowledgeshouldbederivedfromthefactsbyinduction.Theproblemariseswhenweposethequestionofhowtheknowledgeappealedtowhenjudgingtherelevanceorotherwiseofsomecircumstancestoaphenomenonunderinvestigation(suchastheexpansionofmetals)isitselfvindicated.Ifwedemandthatthatknowledgeitselfistobearrivedatbyinduction,thenourproblemwillrecur,becausethosefurtherinductiveargumentswillthemselvesrequirethespecificationoftherelevantcircumstancesandsoon.Eachinductiveargumentinvolvesanappealtopriorknowledge,whichneedsaninductiveargumenttojustifyit,whichinvolvesanappealtofurtherpriorknowledgeandsooninanever-endingchain.Thedemandthatallknowledgebejustifiedbyinductionbecomesademandthatcannotbemet.

EvenCondition3isproblematicsincelittlescientificknowledgewouldsurvivethedemandthattherebenoknownexceptions.

Theappealofinductivism

Aconciseexpressionoftheinductivistviewofscience,theviewthatscientificknowledgeisderivedfromthefactsbyinductiveinferencewhichwehavediscussed,iscontainedinthefollowingpassagewrittenbyatwentieth-centuryeconomist.

Ifwetrytoimaginehowamindofsuperhumanpowerandreach,butnormalsofarasthelogicalprocessesofitsthoughtareconcerned,wouldusethescientificmethod,theprocesswouldbeasfollows:First,allfactswouldbeobservedandrecorded,withoutselectionoraprioriguessastotheirrelativeimportance.Secondly,theobservedandrecordedfactswouldbeanalyzed,comparedandclassified,withouthypothesisorpostulates,otherthanthosenecessarilyinvolvedinthelogicofthought.Third,fromthisanalysisofthefacts,generalizationswouldbeinductivelydrawnastotherelations,classificatoryorcausal,betweenthem.Fourth,furtherresearchwouldbedeductiveaswellasinductive,employinginferencesfrompreviouslyestablishedgeneralizations.

Testinghypotheses:Deductivelogic

Letusnextexplorehowthepositivistviewsthelogicoftesting.Itissummarizedinfigure2.Thelawsandtheoriesthatmakeupscientificknowledgearederivedbyinductionfromafactualbasissuppliedbyobservationandexperiment.Oncesuchgeneralknowledgeisavailable,itcanbedrawnontomakepredictionsandofferexplanations.

Lawsandtheories

Factsacquiredthroughobservations Predictionsandexplanations

Considerthefollowingargument:

1.Fairlypurewaterfreezesatabout0?C(ifgivensufficienttime).

2.Mycarradiatorcontainsfairlypurewater.

3.Ifthetemperaturefallswellbelow0°C,thewaterinmycarradiatorwillfreeze(ifgivensufficienttime).

Herewehaveanexampleofavalidlogicalargument